linux-kernel - Re: [PATCH v2 11/11] KVM: SVM: Drop support for CPUs without NRIPS (NextRIP Save) support

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Message-ID: <656aaf33-8c70-8b06-2cdc-fd2685a1348b@maciej.szmigiero.name>
Date:   Tue, 26 Apr 2022 01:00:54 +0200
From:   "Maciej S. Szmigiero" <mail@...iej.szmigiero.name>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Maxim Levitsky <mlevitsk@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v2 11/11] KVM: SVM: Drop support for CPUs without NRIPS
 (NextRIP Save) support

On 23.04.2022 04:14, Sean Christopherson wrote:
> Drop support for CPUs without NRIPS along with the associated module
> param.  Requiring NRIPS simplifies a handful of paths in KVM, especially
> paths where KVM has to do silly things when nrips=false but supported in
> hardware as there is no way to tell the CPU _not_ to use NRIPS.
> 
> NRIPS was introduced in 2009, i.e. every AMD-based CPU released in the
> last decade should support NRIPS.
> 
> Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
> Not-signed-off-by: Sean Christopherson <seanjc@...gle.com>

To be honest, I think completely removing KVM support (rather than just nSVM)
for these older AMD CPUs is a bit too much.
I totally envision complaints coming after this change reaches distro kernels.

After all, even older Yonah parts remain supported on the VMX side.

Thanks,
Maciej